Aqueous dispersions of polymers, for example copolymers based on conjugated, aliphatic dienes and vinyl aromatic compounds are known (see, for example, DE-A 26 02 445, DE-A 26 02 444, U.S. Pat. No. 3,575,913). The aqueous polymer dispersions are conventionally stabilised using known emulsifiers or protective colloids which are known to the person skilled in the art (Houben-Weyl, Methoden der org. Chemie, Vol. XIV/1, 1961, Stuttgart). Examples of these are polyglycol ethers, sulphonated paraffin hydrocarbons, higher alkyl sulphates (such as, for example, lauryl sulphate), alkali metal salts of fatty acids, such as sodium stearate or sodium oleate, salts of sulphonated arylaromatics such as, for example, sodium dodecylbenzenesulphonate, ethoxylated C4-C12 alkylphenols and their sulphonation products and esters of sulphosuccinic acid. Examples of protective colloids are alkyl-hydroxyalkyl celluloses, partly or completely hydrolysed polyvinyl alcohols and copolymers of the same, acrylic acid, homopolymers and copolymers and partly neutralised salts of the same, acrylamide copolymers, polyacrylate copolymers and salts of the same, carboxyalkyl celluloses such as, for example, carboxymethyl celluloses and salts thereof, and water-soluble starch derivatives. Other examples of known emulsifiers include sulphuric acid half-ester of an ethoxylated fatty alcohol, as described in document U.S. Pat. No. 5,910,534.
Such polymers, especially copolymers often referred to as “Styrene-Butadiene” copolymers, can be used as binders in for paper coatings.
There is a need for dispersions of polymers and/or processes for making the same, that have the following properties:
toxicological or ecotoxicological profile of emulsifiers considered as good, especially considered as better than the profile of diphenylene oxide disulfonates.
a low grit amount. Grit is a consequence of coarse particles in the polymer dispersion that alter the aspect once it is coated. If grit is too high the coating has a bad aspect, thus the polymer dispersion might have to be filtered, which is long and expensive. Grit is also referred to as coagulum.
a high whiteness and/or low color index (low yellow index),
a high ability of a coating to remain on paper upon printing processing, for example upon printing. A high dry pick-up value can typically represent this ability.
and/or combinations or compromise of the above, such as color and dirt pick-up.
Further properties that are of value, alone and/or combined with the above include:
acceptable rheological properties for example to allow high speed coating,
good particle size control during polymerization.